Many specialized terms and abbreviations are used in the communications arts. At least some of the following are referred to within the text that follows, such as in this background and/or the description sections. Thus, the following terms and abbreviations are herewith defined:
3GPP 3rd Generation Partnership Project
ARQ Automatic Repeat-reQuest
C Compressed LCH-ID indicator
CDMA Code Division Multiple Access
DL Downlink
F Flag bit
HARQ Hybrid Automatic-Repeat-reQuest
HI Header Indicator
ID Identifier
IMT-2000 International Mobile Telecommunication-2000
IP Internet Protocol
ITU International Telecommunication Union
LCH Logical Channel
LI Length Indicator
LTE Long Term Evolution
MAC Medium Access Control
OSI Open Systems Interconnection
PDU Protocol Data Unit
RAN Radio Access Network
RRC Radio Resource Control
SDU Service Data Unit
SI Segmentation Indicator
SRB Signaling Radio Bearer
SW Stop and Wait
TSG Technical Specification Group
TSN Transmission Sequence Number
UE User Equipment
UMTS Universal Mobile Telecommunications System
UTRA UMTS Terrestrial Radio Access
UTRAN UMTS Terrestrial Radio Access Network
VoIP Voice over IP
Wi-Fi Wireless Fidelity
WiMAX Worldwide Interoperability for Microwave Access
WG Working Group
Communication forms the backbone of today's information-oriented society. Communications may be transmitted over wireless or wired channels using, for example, radio frequency radiation, light waves, combinations thereof, and so forth. The usability and capacity of such communications is typically limited by the bandwidth of the communications channel. The bandwidth of a communications channel may be limited by the finite nature of the electromagnetic spectrum.
The available bandwidth of a communications channel, even given a finite allocation of the electromagnetic spectrum, may be increased by adopting any of a number of different schemes. This is because certain schemes enable more information to be communicated in a given spectrum allocation. Such efficient utilization of spectrum can reduce the cost of communication services being provided, can enable richer communication services to be provided, or both. Consequently, modern communications standards often attempt to efficiently utilize spectrum.
The evolution of communication standards, including telecommunication system standards, is currently focused on packet access technologies to increase the efficient utilization of spectrum. A principle of packet access technologies is that small data units or packets carry data over an underlying wireless or wired network (or communication medium) while some meta-data or packet header describes the data being communicated. The content of the packet header depends on the type of transferred data and the context of use.
An example of a telecommunications standard is the International Mobile Telecommunication-2000 (IMT-2000) family of standards, which are specified by the International Telecommunication Union (ITU) Radio communication sector (ITU-R). The IMT-2000 protocol architecture model defines service interfaces between different protocol layers as well as sub-layers thereof. Following commonly-accepted conventions, the packets that are exchanged between peer entities (e.g., those within the same layer) are called Protocol Data Units (PDU) whereas the packets that are exchanged between two entities from different layers are called Service Data Units (SDU).
One type of PDU corresponds to those PDUs that are carried on a Medium Access Control (MAC) layer; these are termed MAC PDUs. MAC PDUs often have predefined header formats. For example, a MAC header typically includes at least the following types of information: Logical Channel Identifier (LCH-ID), Transmission Sequence Number (TSN), and Length Indicator (LI). LCH-IDs indicate how different MAC services are addressed or referenced because multiple MAC services may be simultaneously extant. TSNs provide an appropriate PDU numbering because PDUs are sometimes lost or received out-of-order (e.g., due to HARQ retransmissions). The LI information indicates a length of the associated data.
FIG. 1 is an existing 24-bit header format 101 for MAC PDUs in accordance with IMT-2000. As illustrated, example header format 101 includes five fields. These five fields are: LCH-ID, LI, TSN, Segmentation Indicator (SI), and Flag (F). The LCH-ID field is four bits in length. The LI field is 11 bits. The TSN field is 6 bits, and the SI field is 2 bits. The F field is a one-bit flag. This existing header format 101 is therefore 24 bits long.
In certain environments, the two bits of the SI field indicate whether or not the associated data payload is segmented. If the data payload is segmented, the SI field may also indicate whether the associated data corresponds to a first segment, a middle segment, or a final segment. The F flag bit indicates whether the following information constitutes padding or a new header.
Usually, the relative amount of overhead consumed by each header as compared to the actual size of the associated payload is insignificant so long as the packets are large. This is normally the case for relatively high data rate services. The situation is different, however, for relatively low data rate services in which the packets are typically smaller. An example of a relatively low data rate service is Voice over IP (VoIP). In other words, header size can adversely impact communication efficiency, especially with relatively low data rate services.
This need has been addressed in the 3rd Generation Partnership Project (3GPP). Also, some proposals have been discussed within the Technical Specification Group (TSG) Radio Access Network (RAN) Working Groups (WG), which are responsible for Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) and Evolved UTRA standardization.
For example, one proposed approach is to utilize the UTRAN retransmission protocol structure. The UTRAN retransmission protocol structure is composed of multiple parallel Stop-and-Wait (SW) Automatic Repeat-reQuest (ARQ) processes. In short, this approach involves reserving one ARQ process for low data-rate services, such as VoIP. Consequently, there is no need to use a header in the MAC PDU because the receiver can infer the LCH-ID from the ARQ process ID. Also, because SW ARQ protocols do not reorder packets, there is accordingly no need for TSNs.
Unfortunately, this proposed approach entails a number of deficiencies. Specifically, reserving one ARQ process for one specific service, e.g. VoIP, has the following downsides. Firstly, the peak data rate is limited because only one process is available. Secondly, the arrival process for incoming data units is typically characterized by a level of uncertainty inasmuch as data units sometimes arrive in clusters with long gaps between the clusters. The reserved ARQ process is therefore occasionally idle—i.e., the reserved ARQ resource is sometimes unused, which has a negative impact on other services and resource efficiency as well as on peak data rates.
Consequently, there is a continuing need to address the problems and deficiencies in the current state of the art that relate to the overhead inefficiencies of low data rate services. Such deficiencies and other needs are addressed by one or more of the various described embodiments of the present invention.